This invention relates generally to electromagnetic proximity detectors and more particularly to devices for testing such magnetic proximity detectors which are used with ski lifts or tramways for detecting a derope condition of the cable utilized as a haul rope for the lift system.
Magnetic proximity detectors are commonly used on ski lifts and tramways for detecting a derope condition of the steel cable used as a haul line or haul rope. An example of such a detector is illustrated in U.S. Pat. No. 4,271,763, issued on Jun. 9, 1981. This patent also discloses a testing device.
The testing device shown in this patent consists of a non-ferromagnetic sleeve which is provided in substantially symmetric halves which are fastened together with non-magnetic bolts over the lift cable. The sleeve is relatively thin so as not to significantly raise the cable away from the detector when riding thereover and the sleeve is further provided with circular shaped magnets which are positioned in two circumferential rows and the permanent magnets are chosen and positioned to form a north pole and a south pole so as to disrupt and modify the electromagnetic field of the detector when passing thereover to send a derope detector signal for testing the electromagnetic detector.
While this test device is effective, it is nevertheless difficult and expensive to manufacture and depends upon the attached permanent magnets not becoming dislodged from the sleeve.
It is accordingly an object of the present invention to provide such a safety testing device for electromagnetic proximity detectors used on ski lifts and tramways which is devoid of these mentioned problems or inadequacies.
The apparatus of the present invention is provided for testing a cable derope magnetic proximity detector which is positioned adjacent a cable sheave or sheave assembly on a cable operated ski lift. The testing apparatus is comprised of a non-ferromagnetic sleeve having an inner diameter for mating the outside diameter of the steel lift cable and is dimensioned in length and thickness in amounts sufficient to raise the cable simultaneously away from the detector and the adjacent sheave or sheave assembly whereby the detector will indicate a derope condition. The sleeve is flexible and preferably made of plastic, including hard rubber, and the sleeve is provided with tapered ends to provide an easy ride-up transition onto the sheaves. The sleeve is provided in two longitudinal split halves and may be readily secured in place over the cable with tape.
Accordingly, in order to test the magnetic proximity detectors, the sleeve is temporarily secured over the cable and the ski lift or tramway is operated to thereby move the sleeve with the cable over the detector and adjacent sheave or sheave assembly in order to simulate a derope condition and thereby cause the magnetic proximity detector to set off an alarm. By design, the testing device will raise the steel cable haul rope up off the sheave wheels of the sheave assembly to test the proximity switch of the magnetic proximity detector and it will also maintain the haul rope centered on the sheave wheels so that deropement does not occur during testing. Also, if the cable twists, it will not effect the testing device, as can be a problem with prior art testing devices.